There is currently great interest in the development of molecular or nanoscale electrical devices. To this end, much effort has been devoted to developing nanoscale electronic devices using organic materials including small molecules and polymers. In addition to providing higher device densities in integrated circuits, polymeric electronic devices may be more physically flexible and more cost and processing-efficient than conventional inorganic semiconductor devices.
In such nanoscale electronic devices, single molecular layers may form active elements in the device. The efficient formation of reliable electrical contacts to the molecular layer is therefore an important aspect in the commercial production of nanoscale devices. The molecules are typically fixed at one end to a conducive substrate that forms one electrical contact for the device, and to a metal layer on the other end to form a second electrical contact. Conventional processes for depositing the metal onto the molecules include treatment with a metal containing solution, to produce a colloidal metal layer, or evaporation of the metal onto the molecules, to produce an evaporated metal layer.
There may be, however, gaps between the molecules. In addition, the molecules are typically able to rotate about the first electrical contact. Both the presence of gaps, and the ability of molecules to rotate, impede the attachment of the deposited metal layer to form the second electrical contact. Some of the deposited metal, for example, goes between the gaps between molecules, resulting in an electrical short circuit between the conductive substrate and metal layer.
Furthermore, methods based on treatments with solutions of colloidal metal particles do not produce connections to all the molecules because solution-transported metal particles may attach to randomly distributed single molecules rather than to substantially all of the molecules. Methods based on the direct evaporation of metal onto the molecules are also problematic, because the high kinetic energy of the metal atoms striking the molecules may destroy or alter the structure of the molecular layer. Efforts to reduce the deleterious effects of direct evaporation, such as low temperature evaporation, or shallow angle evaporation, have not improved the production of non-defective devices to satisfactory levels. As a result, conventional processes for the deposition of the metal layer continue to produce a large number of nonfunctional devices, as indicated, for example, by the devices having an undesirably low resistance across the molecular layer. Of all devices produced in a typical conventional process, for instance, only 2% may be functional.
Therefore, previously proposed methods of attaching electrical contacts to a layer of molecules lack the desired reliability demanded by today's electronics industry. Accordingly, what is needed in the art is a method of forming such contacts, thereby increasing the efficient production of nanoscale electrical devices, while not experiencing the problems associated with previous methods.